Generally, a concrete transport vehicle has a mixer unit that includes a rotatable mixing drum in which concrete can be mixed and transported. Concrete is usually loaded and unloaded through the drum mouth, which is angled upwards along an inclined axis. The typical concrete truck also includes a hopper for feeding concrete into the drum and a chute for channeling concrete out of the drum. The hopper and chute are normally aligned adjacent the mouth of the drum with the chute positioned below the hopper. As the concrete transport vehicle moves, the mixer unit tends to flex and shift. When combined with the constant rotation of the drum, this flexing and shifting provides for rather irregular positioning of the drum mouth. When the mixer unit contains concrete, it is not uncommon for some concrete material to be inadvertently discharged from the drum mouth, especially when the concrete truck is moving especially up hill. Consequently, concrete may fall from the mixing unit onto roadways and construction sites, resulting in a loss of valuable concrete as well as the potential for a safety hazard or at least a nuisance. Even in light of the potential consequences of inadvertent discharge, little past progress has been made to reduce effectively the likelihood of such discharge due to the irregularity of the movement of the mixing drum. Consequently, there is a need for an apparatus that helps to reduce the occurrence of inadvertent discharge of concrete material from the drum mouth of a mixing unit, as well as a concrete transport vehicle that incorporates the principles of such a device.